What is the difference between Ni-NTA Agarose and Ni-NTA Superflow?

The binding capacity of both resins is the same: up to 50mg/ ml mg 6xHis-tagged protein per ml of resin (2500 nmol @ ~20 kDa). The difference between them is the bead support, which determines pressure resistance and flow rate:

Ni-NTA Agarose:

Sepharose CL-6B (bead size 45–165 µm)
max. volumetric: 0.5–1.0 ml/min
max. pressure: 2.8 psi/(0.2bar)
for use with gravity flow only

Ni-NTA Superflow:

Superflow (bead size 60–160 µm)
max. volumetric: 20 ml/min
max. pressure: 140 psi/(10bar)
for use with gravity flow or FPLC

You can find a detailed comparison table in the Appendix at the back of the QIAexpressionist Handbook under the title 'Ni-NTA Matrices'.